package aoj.no_1100;

import java.util.Scanner;

import lib.Geo;

public class No_1100 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int count = 1;
		while(true) {
			int iVertex = sc.nextInt();
			if(iVertex == 0)
				break;
			
			int x[] = new int[iVertex];
			int y[] = new int[iVertex];
			for(int i = 0; i < iVertex; i++) {
				x[i] = sc.nextInt();
				y[i] = sc.nextInt();
			}
			
			double area = 0.0;
			
			for(int i = 0; i < iVertex - 2; i++) {
				area += Geo.exteriorProduct(x[i+1]-x[0], y[i+1]-y[0], x[i+2]-x[0], y[i+2]-y[0]);
			}
			
			System.out.printf("%d %.1f\n", count, Math.abs(area)/2.0);
			count++;
		}
	}
}
